As is known in the art, many semiconductor devices require heating of various structures on the semiconductor. For example field effect transistors (FETs) use ohmic contacts for source contacts and drain contacts. One type of FET is a Gallium Nitride High Electron Mobility Transistor (HEMT) having source and drain electrodes in ohmic contact with an Aluminum Gallium Nitride (AlGaN) semiconductor layer. GaN and AlGaN are wideband gap semiconductor. It is difficult to make a reliable ohmic contact with good metal morphology on these wide band gap semiconductors. Many approaches have been tried with a variety of metal mixtures on GaN and AlGaN such as Ti/Al/Ni/Au, Ti/Al/Ti/Au, Ti/Al/Mo/Au, Ti/Al/Ta/Au and Ta/Al/Ta. Variations of the structures had been tried by changing the thickness of each layer in the stack. These metal schemes require high alloy temperature, for example, an alloy temperature in a range of 600° C. to over 900° C. to form the ohmic contact.
One technique used to provide the required high alloy temperature is called a Rapid Thermal Anneal (RTA) process. In an RTA alloy process, the wafer having many FET structures to be processed is placed inside the RTA, as shown in FIG. 2. The heating lamps, such as, Tungsten Halogen heating lamps radiating energy primarily in the visible radiation band and extending in the Infrared bands and slightly in the ultraviolet bands, are used to heat the ohmic metal by radiation.